Reference signal sequence identification in wireless communications

ABSTRACT

Methods, systems, and devices for wireless communications are described in which a base station may provide an indication of a reference signal to be used in demodulation of a π/2 BPSK modulation scheme for communications between a UE and the base station. The base station may indicate whether a first type of reference signal or a second type of reference signal is to be transmitted. The second type of reference signal may be a π/2 BPSK DMRS that has a reference signal sequence that has a lower PAPR. The second type of reference signal sequence may be a power deboosted version of the first reference signal sequence. The indication from the base station of the type of reference signal may be provided via RRC signaling, such as a cell-specific RRC transmission or a UE-specific RRC transmission.

CROSS REFERENCE

The present Application for Patent claims the benefit of U.S.Provisional Patent Application No. 62/693,860 by HUANG et al., entitled“REFERENCE SIGNAL SEQUENCE IDENTIFICATION IN WIRELESS COMMUNICATIONS,”filed Jul. 3, 2018, assigned to the assignee hereof, and expresslyincorporated herein.

BACKGROUND

The following relates generally to wireless communications, and toreference signal sequence identification in wireless communications.

Wireless communications systems are widely deployed to provide varioustypes of communication content such as voice, video, packet data,messaging, broadcast, and so on. These systems may be capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., time, frequency, and power). Examples of suchmultiple-access systems include fourth generation (4G) systems such asLong Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, orLTE-A Pro systems, and fifth generation (5G) systems which may bereferred to as New Radio (NR) systems. These systems may employtechnologies such as code division multiple access (CDMA), time divisionmultiple access (TDMA), frequency division multiple access (FDMA),orthogonal frequency division multiple access (OFDMA), or discreteFourier transform-spread-OFDM (DFT-S-OFDM). A wireless multiple-accesscommunications system may include a number of base stations or networkaccess nodes, each simultaneously supporting communication for multiplecommunication devices, which may be otherwise known as user equipment(UE).

SUMMARY

The described techniques relate to improved methods, systems, devices,and apparatuses that support reference signal sequence identification inwireless communications. Various described techniques provide forindicating a reference signal to be used in demodulation of a π/2 binaryphase shift keying (BPSK) modulation scheme for communications between auser equipment (UE) and a base station. In some cases, the base stationmay indicate a first type of reference signal or a second type ofreference signal that is to be transmitted. The indication from the basestation of the type of reference signal may be provided via radioresource control (RRC) signaling, such as a cell-specific RRCtransmission that indicates the type of reference signal sequence to beused by each UE in a cell served by the base station (e.g., a systeminformation block (SIB) transmission, an other system information (OSI)transmission, or a remaining minimum system information (RMSI)transmission), or a UE-specific RRC transmission provided to each UE.

The first type of reference signal may be based on a Zadoff-Chu (ZC)sequence, in some examples, that is usable by all UEs served by the basestation, and the second type of reference signal may be usable by fewerthan all UEs served by the base station (e.g., UEs that are capable ofoperating according to a newer release of a wireless communicationsstandard). In some cases, the second type of reference signal has areference signal sequence that has a lower peak to average power ratio(PAPR) than the first type of reference signal. In other cases, thesecond type of reference signal sequence may be a power deboostedversion of the first reference signal sequence (e.g., a power deboostedZC sequence).

A method of wireless communication at a UE is described. The method mayinclude establishing a connection with a base station that uses a π/2BPSK modulation scheme for at least a portion of wireless communicationswith the base station, receiving, from the base station, an indicationof a type of reference signal sequence to be included withintransmissions that use the π/2 BPSK modulation scheme, generating areference signal based on the indication of the type of reference signalsequence, and transmitting the reference signal within communicationsthat use the π/2 BPSK modulation scheme.

An apparatus for wireless communication at a UE is described. Theapparatus may include a processor, memory in electronic communicationwith the processor, and instructions stored in the memory. Theinstructions may be executable by the processor to cause the apparatusto establish a connection with a base station that uses a π/2 BPSKmodulation scheme for at least a portion of wireless communications withthe base station, receive, from the base station, an indication of atype of reference signal sequence to be included within transmissionsthat use the π/2 BPSK modulation scheme, generate a reference signalbased on the indication of the type of reference signal sequence, andtransmit the reference signal within communications that use the π/2BPSK modulation scheme.

Another apparatus for wireless communication at a UE is described. Theapparatus may include means for establishing a connection with a basestation that uses a π/2 BPSK modulation scheme for at least a portion ofwireless communications with the base station, receiving, from the basestation, an indication of a type of reference signal sequence to beincluded within transmissions that use the π/2 BPSK modulation scheme,generating a reference signal based on the indication of the type ofreference signal sequence, and transmitting the reference signal withincommunications that use the π/2 BPSK modulation scheme.

A non-transitory computer-readable medium storing code for wirelesscommunication at a UE is described. The code may include instructionsexecutable by a processor to establish a connection with a base stationthat uses a π/2 BPSK modulation scheme for at least a portion ofwireless communications with the base station, receive, from the basestation, an indication of a type of reference signal sequence to beincluded within transmissions that use the π/2 BPSK modulation scheme,generate a reference signal based on the indication of the type ofreference signal sequence, and transmit the reference signal withincommunications that use the π/2 BPSK modulation scheme.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the indication of the type ofreference signal sequence indicates a first type of reference signalsequence or a second type of reference signal sequence. In some examplesof the method, apparatuses, and non-transitory computer-readable mediumdescribed herein, the second type of reference signal sequence may havea lower PAPR than the first type of reference signal. In some examplesof the method, apparatuses, and non-transitory computer-readable mediumdescribed herein, the second type of reference signal sequence may be apower deboosted version of the first sequence. In some examples of themethod, apparatuses, and non-transitory computer-readable mediumdescribed herein, the first type of reference signal sequence may be aZC sequence and the second type of reference signal sequence may be apower deboosted ZC sequence or a π/2 BPSK demodulation reference signal(DMRS) sequence. In some examples of the method, apparatuses, andnon-transitory computer-readable medium described herein, the indicationof the type of reference signal sequence indicates the power deboostedZC sequence and an amount of power deboosting to apply relative to datatransmissions that use the π/2 BPSK modulation scheme.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the indication from the basestation may be received via RRC signaling. In some examples of themethod, apparatuses, and non-transitory computer-readable mediumdescribed herein, the RRC signaling may be a cell-specific RRCtransmission that indicates the type of reference signal sequence to beused by each UE in a cell served by the base station. In some examplesof the method, apparatuses, and non-transitory computer-readable mediumdescribed herein, the cell-specific RRC transmission includes a SIBtransmission, an OSI transmission, or an RMSI transmission from the basestation. In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the RRC signaling may be aUE-specific RRC transmission that indicates the type of reference signalsequence to be used by the UE.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for transmitting acapability indication to the base station that indicates supported typesof reference signals at the UE, and where the indication of the type ofreference signal may be received responsive to the capabilityindication. In some examples of the method, apparatuses, andnon-transitory computer-readable medium described herein, the indicationof the type of reference signal sequence provides an initial type ofreference signal sequence, and where the UE may further may perform orinclude features, means, or instructions for transmitting a capabilityindication to the base station that indicates supported types ofreference signals at the UE, receiving, responsive to the capabilityindication, a second indication of the type of reference signal sequenceto be included within transmissions that use the π/2 BPSK modulationscheme, and generating a reference signal based on the second indicationof the type of reference signal sequence.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the generating the referencesignal may include operations, features, means, or instructions foridentifying a set of allocated resource blocks and a number of theallocated resource blocks for at least a first transmission using theπ/2 BPSK modulation scheme, determining a bit sequence length for thereference signal corresponding to the number of allocated resourceblocks, and generating the reference signal based on a bit sequencehaving the bit sequence length.

A method of wireless communication at a base station is described. Themethod may include establishing a connection with at least a first UEthat uses a π/2 BPSK modulation scheme for at least a portion ofwireless communications with the first UE, transmitting an indication ofa type of reference signal sequence to be included within transmissionsof at least the first UE that use the π/2 BPSK modulation scheme,receiving a transmission from at least the first UE that uses the π/2BPSK modulation scheme and that includes a reference signal based on theindication of the type of reference signal sequence, and demodulatingthe transmission based on the reference signal.

An apparatus for wireless communication at a base station is described.The apparatus may include a processor, memory in electroniccommunication with the processor, and instructions stored in the memory.The instructions may be executable by the processor to cause theapparatus to establish a connection with at least a first UE that uses aπ/2 BPSK modulation scheme for at least a portion of wirelesscommunications with the first UE, transmit an indication of a type ofreference signal sequence to be included within transmissions of atleast the first UE that use the π/2 BPSK modulation scheme, receive atransmission from at least the first UE that uses the π/2 BPSKmodulation scheme and that includes a reference signal based on theindication of the type of reference signal sequence, and demodulate thetransmission based on the reference signal.

Another apparatus for wireless communication at a base station isdescribed. The apparatus may include means for establishing a connectionwith at least a first UE that uses a π/2 BPSK modulation scheme for atleast a portion of wireless communications with the first UE,transmitting an indication of a type of reference signal sequence to beincluded within transmissions of at least the first UE that use the π/2BPSK modulation scheme, receiving a transmission from at least the firstUE that uses the π/2 BPSK modulation scheme and that includes areference signal based on the indication of the type of reference signalsequence, and demodulating the transmission based on the referencesignal.

A non-transitory computer-readable medium storing code for wirelesscommunication at a base station is described. The code may includeinstructions executable by a processor to establish a connection with atleast a first UE that uses a π/2 BPSK modulation scheme for at least aportion of wireless communications with the first UE, transmit anindication of a type of reference signal sequence to be included withintransmissions of at least the first UE that use the π/2 BPSK modulationscheme, receive a transmission from at least the first UE that uses theπ/2 BPSK modulation scheme and that includes a reference signal based onthe indication of the type of reference signal sequence, and demodulatethe transmission based on the reference signal.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the indication of the type ofreference signal sequence indicates a first type of reference signalsequence or a second type of reference signal sequence. In some examplesof the method, apparatuses, and non-transitory computer-readable mediumdescribed herein, the second type of reference signal sequence may havea lower PAPR than the first type of reference signal. In some examplesof the method, apparatuses, and non-transitory computer-readable mediumdescribed herein, the second type of reference signal sequence may be apower deboosted version of the first sequence. In some examples of themethod, apparatuses, and non-transitory computer-readable mediumdescribed herein, the first type of reference signal sequence may be aZC sequence and the second type of reference signal sequence may be apower deboosted ZC sequence or a π/2 BPSK DMRS sequence. In someexamples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the indication of the type ofreference signal sequence indicates the power deboosted ZC sequence andan amount of power deboosting to apply relative to data transmissionsthat use the π/2 BPSK modulation scheme.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the indication of the type ofreference signal sequence may be transmitted via RRC signaling. In someexamples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the RRC signaling may be acell-specific RRC transmission that indicates the type of referencesignal sequence to be used by each UE in a cell served by the basestation. In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the cell-specific RRCtransmission includes a SIB transmission, an OSI transmission, or a RMSItransmission. In some examples of the method, apparatuses, andnon-transitory computer-readable medium described herein, the RRCsignaling may be a UE-specific RRC transmission that indicates the typeof reference signal sequence to be used by the first UE, and where oneor more other UEs use a different type of reference signal sequence fortransmissions that use the π/2 BPSK modulation scheme.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for receiving, from thefirst UE, a capability indication that indicates supported types ofreference signals at the UE, and where the indication of the type ofreference signal sequence may be transmitted to the first UE responsiveto the capability indication. In some examples of the method,apparatuses, and non-transitory computer-readable medium describedherein, the indication of the type of reference signal sequence providesan initial type of reference signal sequence, and the method,apparatuses, and non-transitory computer-readable medium describedherein may further include operations, features, means, or instructionsfor receiving, from the first UE, a capability indication that indicatessupported types of reference signals at the UE; selecting, responsive tothe capability indication, the type of reference signal sequence to beincluded within transmissions that use the π/2 BPSK modulation schemeand transmitting a second indication to the first UE of a type ofreference signal sequence to be included within transmissions of atleast the first UE that use the π/2 BPSK modulation scheme, where one ormore subsequent communications with the first UE may be based on thesecond indication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a system for wireless communicationsthat supports reference signal sequence identification in wirelesscommunications in accordance with aspects of the present disclosure.

FIG. 2 illustrates an example of a portion of a wireless communicationssystem that supports reference signal sequence identification inwireless communications in accordance with aspects of the presentdisclosure.

FIG. 3 illustrates another example of a wireless communications systemthat supports reference signal sequence identification in wirelesscommunications in accordance with aspects of the present disclosure.

FIG. 4 illustrates an example of a process flow that supports referencesignal sequence identification in wireless communications in accordancewith aspects of the present disclosure.

FIGS. 5 and 6 show block diagrams of devices that support referencesignal sequence identification in wireless communications in accordancewith aspects of the present disclosure.

FIG. 7 shows a block diagram of a communications manager that supportsreference signal sequence identification in wireless communications inaccordance with aspects of the present disclosure.

FIG. 8 shows a diagram of a system including a device that supportsreference signal sequence identification in wireless communications inaccordance with aspects of the present disclosure.

FIGS. 9 and 10 show block diagrams of devices that support referencesignal sequence identification in wireless communications in accordancewith aspects of the present disclosure.

FIG. 11 shows a block diagram of a communications manager that supportsreference signal sequence identification in wireless communications inaccordance with aspects of the present disclosure.

FIG. 12 shows a diagram of a system including a device that supportsreference signal sequence identification in wireless communications inaccordance with aspects of the present disclosure.

FIGS. 13 through 17 show flowcharts illustrating methods that supportreference signal sequence identification in wireless communications inaccordance with aspects of the present disclosure.

DETAILED DESCRIPTION

In some wireless communications systems, a transmitter, such as a UE ora base station, may transmit one or more reference signals to provide areceiver, such as a UE or a base station, with an amplitude and a phasereference for performing channel estimation of a wireless channel. Thereceiver may use the channel estimate to remove amplitude and/or phasedistortion to a signal caused by transmission of the signal via thewireless channel. In some LTE and NR systems, for example, a transmittermay generate a reference signal by performing quadrature phase shiftkeying (QPSK) modulation on a Zadoff-Chu (ZC) sequence. pilot tones thattransport a QPSK -based reference signal may have a large peak toaverage power ratio (PAPR), and may not be suitable for use in some NRsystems. Moreover, such reference signals may cause tones that transportreference signals to have a PAPR that may exceed a PAPR of tones thattransport data.

In some cases, larger PAPRs or large differences in PAPRs betweenreference signal tones and data tones may cause a power amplifier (PA)at a UE to have a gain that is set according to the higher PAPR of thereference signal, which may result in data tones with lower gain.Further, in some 5G or NR systems, a π/2 binary phase shift keying(BPSK) modulation scheme may be implemented from some communicationsbetween a UE and a base station, in which the BPSK constellation ofalternating tones is phase shifted by 90 degrees. Such techniquesprovide a lower PAPR relative to standard BPSK modulation. However, incases where a reference signal that uses the ZC sequence is includedwith transmissions, the PAPR of the reference signal may result inreduced PA gain.

In some examples, in order to allow a receiving device to have higher PAgain, a second type of reference signal may be implemented in additionor alternatively to a first type of reference signal that includes a ZCsequence that is transmitted at a same power level as data tones. Thus,implementing the second type of reference signal may enhance reliabilityfor transmissions of data tones due to being transmitted at highergains. In some cases, different UEs may have different capabilities fortransmitting and receiving the second type of reference signal. Forexample, UEs deployed in some NR systems may be capable of transmittingand receiving the first type of reference signal and not the second typeof reference signal, while other UEs may be capable of transmitting andreceiving both the first type of reference signal and the second type ofreference signal.

Various aspects of the present disclosure provide techniques forindicating a reference signal to be used in demodulation of a π/2 BPSKmodulation scheme for communications between the UE and the basestation. In some cases, the base station may indicate whether the firsttype of reference signal or the second type of reference signal is to betransmitted. In some cases, the second type of reference signal may be aπ/2 BPSK demodulation reference signal (DMRS) that has a referencesignal sequence with a lower PAPR than the first type of referencesignal (e.g., a ZC sequence). In other cases, the second type ofreference signal sequence may be a power deboosted version of the firstreference signal sequence (e.g., a power deboosted ZC sequence). Theindication from the base station of the type of reference signal may beprovided via radio resource control (RRC) signaling, such as acell-specific RRC transmission that indicates the type of referencesignal sequence to be used by each UE in a cell served by the basestation (e.g., a system information block (SIB) transmission, an othersystem information (OSI) transmission, or a remaining minimum systeminformation (RMSI) transmission), or a UE-specific RRC transmissionprovided to each UE.

In some cases, cell-specific RRC signaling may be used to establish aninitial type of reference signal (e.g., the first type of referencesignal) that is to be used by a UE and, after the UE reports acapability for different types of reference signals (e.g., via aphysical uplink shared channel (PUSCH) transmission), the base stationmay transmit UE-specific RRC signaling that indicates a type ofreference signal to use for one or more subsequent transmissions (e.g.,an RRC reconfiguration may indicate which type of reference signal is tobe used, a semi-persistent scheduling (SPS) grant may indicate a type ofreference signal to use for SPS transmissions, etc.). If the indicationfrom the UE-specific RRC is different than the initial type of referencesignal, the indication from the UE-specific RRC may override the initialtype of reference signal.

Aspects of the disclosure are initially described in the context of awireless communications system. Aspects of the disclosure are furtherillustrated by and described with reference to apparatus diagrams,system diagrams, and flowcharts that relate to reference signal sequenceidentification in wireless communications.

FIG. 1 illustrates an example of a wireless communications system 100that supports reference signal sequence identification in wirelesscommunications in accordance with aspects of the present disclosure. Thewireless communications system 100 includes base stations 105, UEs 115,and a core network 130. In some examples, the wireless communicationssystem 100 may be a Long Term Evolution (LTE) network, an LTE-Advanced(LTE-A) network, an LTE-A Pro network, or a New Radio (NR) network. Insome cases, wireless communications system 100 may support enhancedbroadband communications, ultra-reliable (e.g., mission critical)communications, low latency communications, or communications withlow-cost and low-complexity devices.

Base stations 105 may wirelessly communicate with UEs 115 via one ormore base station antennas. Base stations 105 described herein mayinclude or may be referred to by those skilled in the art as a basetransceiver station, a radio base station, an access point, a radiotransceiver, a NodeB, an eNodeB (eNB), a next-generation Node B orgiga-nodeB (either of which may be referred to as a gNB), a Home NodeB,a Home eNodeB, or some other suitable terminology. Wirelesscommunications system 100 may include base stations 105 of differenttypes (e.g., macro or small cell base stations). The UEs 115 describedherein may be able to communicate with various types of base stations105 and network equipment including macro eNBs, small cell eNBs, gNBs,relay base stations, and the like.

Each base station 105 may be associated with a particular geographiccoverage area 110 in which communications with various UEs 115 issupported. Each base station 105 may provide communication coverage fora respective geographic coverage area 110 via communication links 125,and communication links 125 between a base station 105 and a UE 115 mayutilize one or more carriers. Communication links 125 shown in wirelesscommunications system 100 may include uplink transmissions from a UE 115to a base station 105, or downlink transmissions from a base station 105to a UE 115. Downlink transmissions may also be called forward linktransmissions while uplink transmissions may also be called reverse linktransmissions.

The geographic coverage area 110 for a base station 105 may be dividedinto sectors making up only a portion of the geographic coverage area110, and each sector may be associated with a cell. For example, eachbase station 105 may provide communication coverage for a macro cell, asmall cell, a hot spot, or other types of cells, or various combinationsthereof In some examples, a base station 105 may be movable andtherefore provide communication coverage for a moving geographiccoverage area 110. In some examples, different geographic coverage areas110 associated with different technologies may overlap, and overlappinggeographic coverage areas 110 associated with different technologies maybe supported by the same base station 105 or by different base stations105. The wireless communications system 100 may include, for example, aheterogeneous LTE/LTE-A/LTE-A Pro or NR network in which different typesof base stations 105 provide coverage for various geographic coverageareas 110.

The term “cell” refers to a logical communication entity used forcommunication with a base station 105 (e.g., over a carrier), and may beassociated with an identifier for distinguishing neighboring cells(e.g., a physical cell identifier (PCID), a virtual cell identifier(VCID)) operating via the same or a different carrier. In some examples,a carrier may support multiple cells, and different cells may beconfigured according to different protocol types (e.g., machine-typecommunication (MTC), narrowband Internet-of-Things (NB-IoT), enhancedmobile broadband (eMBB), or others) that may provide access fordifferent types of devices. In some cases, the term “cell” may refer toa portion of a geographic coverage area 110 (e.g., a sector) over whichthe logical entity operates.

UEs 115 may be dispersed throughout the wireless communications system100, and each UE 115 may be stationary or mobile. A UE 115 may also bereferred to as a mobile device, a wireless device, a remote device, ahandheld device, or a subscriber device, or some other suitableterminology, where the “device” may also be referred to as a unit, astation, a terminal, or a client. A UE 115 may also be a personalelectronic device such as a cellular phone, a personal digital assistant(PDA), a tablet computer, a laptop computer, or a personal computer. Insome examples, a UE 115 may also refer to a wireless local loop (WLL)station, an Internet of Things (IoT) device, an Internet of Everything(IoE) device, or an MTC device, or the like, which may be implemented invarious articles such as appliances, vehicles, meters, or the like.

Some UEs 115, such as MTC or IoT devices, may be low cost or lowcomplexity devices, and may provide for automated communication betweenmachines (e.g., via Machine-to-Machine (M2M) communication). M2Mcommunication or MTC may refer to data communication technologies thatallow devices to communicate with one another or a base station 105without human intervention. In some examples, M2M communication or MTCmay include communications from devices that integrate sensors or metersto measure or capture information and relay that information to acentral server or application program that can make use of theinformation or present the information to humans interacting with theprogram or application. Some UEs 115 may be designed to collectinformation or enable automated behavior of machines. Examples ofapplications for MTC devices include smart metering, inventorymonitoring, water level monitoring, equipment monitoring, healthcaremonitoring, wildlife monitoring, weather and geological eventmonitoring, fleet management and tracking, remote security sensing,physical access control, and transaction-based business charging.

Some UEs 115 may be configured to employ operating modes that reducepower consumption, such as half-duplex communications (e.g., a mode thatsupports one-way communication via transmission or reception, but nottransmission and reception simultaneously). In some examples half-duplexcommunications may be performed at a reduced peak rate. Other powerconservation techniques for UEs 115 include entering a power saving“deep sleep” mode when not engaging in active communications, oroperating over a limited bandwidth (e.g., according to narrowbandcommunications). In some cases, UEs 115 may be designed to supportcritical functions (e.g., mission critical functions), and a wirelesscommunications system 100 may be configured to provide ultra-reliablecommunications for these functions.

In some cases, a UE 115 may also be able to communicate directly withother UEs 115 (e.g., using a peer-to-peer (P2P) or device-to-device(D2D) protocol). One or more of a group of UEs 115 utilizing D2Dcommunications may be within the geographic coverage area 110 of a basestation 105. Other UEs 115 in such a group may be outside the geographiccoverage area 110 of a base station 105, or be otherwise unable toreceive transmissions from a base station 105. In some cases, groups ofUEs 115 communicating via D2D communications may utilize a one-to-many(1:M) system in which each UE 115 transmits to every other UE 115 in thegroup. In some cases, a base station 105 facilitates the scheduling ofresources for D2D communications. In other cases, D2D communications arecarried out between UEs 115 without the involvement of a base station105.

Base stations 105 may communicate with the core network 130 and with oneanother. For example, base stations 105 may interface with the corenetwork 130 through backhaul links 132 (e.g., via an S1, N2, N3, orother interface). Base stations 105 may communicate with one anotherover backhaul links 134 (e.g., via an X2, Xn, or other interface) eitherdirectly (e.g., directly between base stations 105) or indirectly (e.g.,via core network 130).

The core network 130 may provide user authentication, accessauthorization, tracking, Internet Protocol (IP) connectivity, and otheraccess, routing, or mobility functions. The core network 130 may be anevolved packet core (EPC), which may include at least one mobilitymanagement entity (MME), at least one serving gateway (S-GW), and atleast one Packet Data Network (PDN) gateway (P-GW). The MME may managenon-access stratum (e.g., control plane) functions such as mobility,authentication, and bearer management for UEs 115 served by basestations 105 associated with the EPC. User IP packets may be transferredthrough the S-GW, which itself may be connected to the P-GW. The P-GWmay provide IP address allocation as well as other functions. The P-GWmay be connected to the network operators IP services. The operators IPservices may include access to the Internet, Intranet(s), an IPMultimedia Subsystem (IMS), or a Packet-Switched (PS) Streaming Service.

At least some of the network devices, such as a base station 105, mayinclude subcomponents such as an access network entity, which may be anexample of an access node controller (ANC). Each access network entitymay communicate with UEs 115 through a number of other access networktransmission entities, which may be referred to as a radio head, a smartradio head, or a transmission/reception point (TRP). In someconfigurations, various functions of each access network entity or basestation 105 may be distributed across various network devices (e.g.,radio heads and access network controllers) or consolidated into asingle network device (e.g., a base station 105).

Wireless communications system 100 may operate using one or morefrequency bands, typically in the range of 300 MHz to 300 GHz.Generally, the region from 300 MHz to 3 GHz is known as the ultra-highfrequency (UHF) region or decimeter band, since the wavelengths rangefrom approximately one decimeter to one meter in length. UHF waves maybe blocked or redirected by buildings and environmental features.However, the waves may penetrate structures sufficiently for a macrocell to provide service to UEs 115 located indoors. Transmission of UHFwaves may be associated with smaller antennas and shorter range (e.g.,less than 100 km) compared to transmission using the smaller frequenciesand longer waves of the high frequency (HF) or very high frequency (VHF)portion of the spectrum below 300 MHz.

Wireless communications system 100 may also operate in a super highfrequency (SHF) region using frequency bands from 3 GHz to 30 GHz, alsoknown as the centimeter band. The SHF region includes bands such as the5 GHz industrial, scientific, and medical (ISM) bands, which may be usedopportunistically by devices that can tolerate interference from otherusers.

Wireless communications system 100 may also operate in an extremely highfrequency (EHF) region of the spectrum (e.g., from 30 GHz to 300 GHz),also known as the millimeter band. In some examples, wirelesscommunications system 100 may support millimeter wave (mmW)communications between UEs 115 and base stations 105, and EHF antennasof the respective devices may be even smaller and more closely spacedthan UHF antennas. In some cases, this may facilitate use of antennaarrays within a UE 115. However, the propagation of EHF transmissionsmay be subject to even greater atmospheric attenuation and shorter rangethan SHF or UHF transmissions. Techniques disclosed herein may beemployed across transmissions that use one or more different frequencyregions, and designated use of bands across these frequency regions maydiffer by country or regulating body.

In some cases, wireless communications system 100 may utilize bothlicensed and unlicensed radio frequency spectrum bands. For example,wireless communications system 100 may employ License Assisted Access(LAA), LTE-Unlicensed (LTE-U) radio access technology, or NR technologyin an unlicensed band such as the 5 GHz ISM band. When operating inunlicensed radio frequency spectrum bands, wireless devices such as basestations 105 and UEs 115 may employ listen-before-talk (LBT) proceduresto ensure a frequency channel is clear before transmitting data. In somecases, operations in unlicensed bands may be based on a CA configurationin conjunction with CCs operating in a licensed band (e.g., LAA).Operations in unlicensed spectrum may include downlink transmissions,uplink transmissions, peer-to-peer transmissions, or a combination ofthese. Duplexing in unlicensed spectrum may be based on frequencydivision duplexing (FDD), time division duplexing (TDD), or acombination of both.

In some examples, base station 105 or UE 115 may be equipped withmultiple antennas, which may be used to employ techniques such astransmit diversity, receive diversity, multiple-input multiple-output(MIMO) communications, or beamforming. For example, wirelesscommunications system 100 may use a transmission scheme between atransmitting device (e.g., a base station 105) and a receiving device(e.g., a UE 115), where the transmitting device is equipped withmultiple antennas and the receiving devices are equipped with one ormore antennas. MIMO communications may employ multipath signalpropagation to increase the spectral efficiency by transmitting orreceiving multiple signals via different spatial layers, which may bereferred to as spatial multiplexing. The multiple signals may, forexample, be transmitted by the transmitting device via differentantennas or different combinations of antennas. Likewise, the multiplesignals may be received by the receiving device via different antennasor different combinations of antennas. Each of the multiple signals maybe referred to as a separate spatial stream, and may carry bitsassociated with the same data stream (e.g., the same codeword) ordifferent data streams. Different spatial layers may be associated withdifferent antenna ports used for channel measurement and reporting. MIMOtechniques include single-user MIMO (SU-MIMO) where multiple spatiallayers are transmitted to the same receiving device, and multiple-userMIMO (MU-MIMO) where multiple spatial layers are transmitted to multipledevices.

Beamforming, which may also be referred to as spatial filtering,directional transmission, or directional reception, is a signalprocessing technique that may be used at a transmitting device or areceiving device (e.g., a base station 105 or a UE 115) to shape orsteer an antenna beam (e.g., a transmit beam or receive beam) along aspatial path between the transmitting device and the receiving device.Beamforming may be achieved by combining the signals communicated viaantenna elements of an antenna array such that signals propagating atparticular orientations with respect to an antenna array experienceconstructive interference while others experience destructiveinterference. The adjustment of signals communicated via the antennaelements may include a transmitting device or a receiving deviceapplying certain amplitude and phase offsets to signals carried via eachof the antenna elements associated with the device. The adjustmentsassociated with each of the antenna elements may be defined by abeamforming weight set associated with a particular orientation (e.g.,with respect to the antenna array of the transmitting device orreceiving device, or with respect to some other orientation).

In some cases, the antennas of a base station 105 or UE 115 may belocated within one or more antenna arrays, which may support MIMOoperations, or transmit or receive beamforming. For example, one or morebase station antennas or antenna arrays may be co-located at an antennaassembly, such as an antenna tower. In some cases, antennas or antennaarrays associated with a base station 105 may be located in diversegeographic locations. A base station 105 may have an antenna array witha number of rows and columns of antenna ports that the base station 105may use to support beamforming of communications with a UE 115.Likewise, a UE 115 may have one or more antenna arrays that may supportvarious MIMO or beamforming operations.

In some cases, wireless communications system 100 may be a packet-basednetwork that operate according to a layered protocol stack. In the userplane, communications at the bearer or Packet Data Convergence Protocol(PDCP) layer may be IP-based. A Radio Link Control (RLC) layer may insome cases perform packet segmentation and reassembly to communicateover logical channels. A Medium Access Control (MAC) layer may performpriority handling and multiplexing of logical channels into transportchannels. The MAC layer may also use hybrid automatic repeat request(HARQ) to provide retransmission at the

MAC layer to improve link efficiency. In the control plane, the RadioResource Control (RRC) protocol layer may provide establishment,configuration, and maintenance of an RRC connection between a UE 115 anda base station 105 or core network 130 supporting radio bearers for userplane data. At the Physical (PHY) layer, transport channels may bemapped to physical channels.

In some cases, UEs 115 and base stations 105 may support retransmissionsof data to increase the likelihood that data is received successfully.HARQ feedback is one technique of increasing the likelihood that data isreceived correctly over a communication link 125. HARQ may include acombination of error detection (e.g., using a cyclic redundancy check(CRC)), forward error correction (FEC), and retransmission (e.g.,automatic repeat request (ARQ)). HARQ may improve throughput at the MAClayer in poor radio conditions (e.g., signal-to-noise conditions). Insome cases, a wireless device may support same-slot HARQ feedback, wherethe device may provide HARQ feedback in a specific slot for datareceived in a previous symbol in the slot. In other cases, the devicemay provide HARQ feedback in a subsequent slot, or according to someother time interval.

The term “carrier” refers to a set of radio frequency spectrum resourceshaving a defined physical layer structure for supporting communicationsover a communication link 125. For example, a carrier of a communicationlink 125 may include a portion of a radio frequency spectrum band thatis operated according to physical layer channels for a given radioaccess technology. Each physical layer channel may carry user data,control information, or other signaling. A carrier may be associatedwith a pre-defined frequency channel (e.g., an E-UTRA absolute radiofrequency channel number (EARFCN)), and may be positioned according to achannel raster for discovery by UEs 115. Carriers may be downlink oruplink (e.g., in an FDD mode), or be configured to carry downlink anduplink communications (e.g., in a TDD mode). In some examples, signalwaveforms transmitted over a carrier may be made up of multiplesub-carriers (e.g., using multi-carrier modulation (MCM) techniques suchas orthogonal frequency division multiplexing (OFDM) or DFT-s-OFDM).

The organizational structure of the carriers may be different fordifferent radio access technologies (e.g., LTE, LTE-A, LTE-A Pro, NR,etc.). For example, communications over a carrier may be organizedaccording to TTIs or slots, each of which may include user data as wellas control information or signaling to support decoding the user data. Acarrier may also include dedicated acquisition signaling (e.g.,synchronization signals or system information, etc.) and controlsignaling that coordinates operation for the carrier. In some examples(e.g., in a carrier aggregation configuration), a carrier may also haveacquisition signaling or control signaling that coordinates operationsfor other carriers.

Physical channels may be multiplexed on a carrier according to varioustechniques. A physical control channel and a physical data channel maybe multiplexed on a downlink carrier, for example, using time divisionmultiplexing (TDM) techniques, frequency division multiplexing (FDM)techniques, or hybrid TDM-FDM techniques. In some examples, controlinformation transmitted in a physical control channel may be distributedbetween different control regions in a cascaded manner (e.g., between acommon control region or common search space and one or more UE-specificcontrol regions or UE-specific search spaces).

Wireless communications system 100 may support communication with a UE115 on multiple cells or carriers, a feature which may be referred to ascarrier aggregation (CA) or multi-carrier operation. A UE 115 may beconfigured with multiple downlink CCs and one or more uplink CCsaccording to a carrier aggregation configuration. Carrier aggregationmay be used with both FDD and TDD component carriers.

Wireless communications systems such as an NR system may utilize anycombination of licensed, shared, and unlicensed spectrum bands, amongothers. The flexibility of eCC symbol duration and subcarrier spacingmay allow for the use of eCC across multiple spectrums. In someexamples, NR shared spectrum may increase spectrum utilization andspectral efficiency, specifically through dynamic vertical (e.g., acrossthe frequency domain) and horizontal (e.g., across the time domain)sharing of resources.

In some cases, a base station 105 may provide an indication of areference signal to be used in demodulation of a π/2 BPSK modulationscheme for communications between a UE 115 and the base station 105. Insome cases, the base station 105 may indicate whether a first type ofreference signal or a second type of reference signal is to betransmitted. In some cases, the second type of reference signal may be aspecified π/2 BPSK DMRS that has a reference signal sequence that has alower PAPR than the first type of reference signal (e.g., a ZCsequence). In other cases, the second type of reference signal sequencemay be a power deboosted version of the first reference signal sequence(e.g., a power deboosted ZC sequence). The indication from the basestation 105 of the type of reference signal may be provided via RRCsignaling, such as a cell-specific RRC transmission that indicates thetype of reference signal sequence to be used by each UE 115 in a cellserved by the base station 105 (e.g., a SIB, OSI, or RMSI transmission),or a UE-specific RRC transmission provided to each UE 115. In somecases, an initial type of reference signal may be indicated by the basestation 105 in cell-specific RRC signaling, which may be overridden forone or more UEs 115 using UE-specific RRC signaling.

FIG. 2 illustrates an example of a wireless communications system 200that supports reference signal sequence identification in wirelesscommunications in accordance with aspects of the present disclosure. Insome examples, wireless communications system 200 may implement aspectsof wireless communications system 100. In this example, wirelesscommunications system 200 includes UE 115-a and base station 105-a,which may be respective examples of a UE 115 and a base station 105 asdescribed herein. UE 115-a and base station 105-a may communicate via acommunication link 205. The communication link 205 may be configured foruplink and downlink transmissions.

UE 115-a and base station 105-a may implement techniques for π/2 BPSKmodulation, which may enable transmission of reference signals and datausing a common modulation scheme to achieve a desired PAPR (e.g., a lowPAPR or a PAPR that is less than a PAPR threshold). In some examples, UE115-a and base station 105-a may use π/2 BPSK modulation and the basestation 105-a may indicate a reference signal that the UE 115-a is touse for π/2 BPSK transmissions. As described above, in some cases thebase station 105-a may indicate that a first type of reference signal ora second type of reference signal is to be used for DMRS transmissions.

In some examples, base station 105-a may allocate one or more resourceblocks to the UE 115-a from a system bandwidth for an uplink or downlinktransmission. The system bandwidth may be divided into a set of resourceblocks that may be allocated for uplink and/or downlink transmission. Atime duration of the resource block may correspond to a transmissiontime interval (TTI) (e.g., a mini-slot, a slot, a subframe, a frame, orthe like), and the base station 105-a may allocate the resource blocksto one or more UEs 115 of the wireless communications system 100 in eachTTI. In some examples, a resource block may correspond to a definednumber of symbol periods and a defined number of subcarriers of acarrier. A resource block may correspond to a set of resource elements,and a resource element may include one subcarrier and one symbol period.Each subcarrier may be a radio frequency used for symbol modulation andmay be spaced apart from one another in frequency by a fixed amount. Insome examples, a resource block may be the smallest set oftime-frequency resources that may be allocated to a UE 115.

Base station 105-a may determine a resource block allocation 210 for UE115-a. Base station 105-a may determine which resource blocks, andcorresponding REs and subcarriers, within the system bandwidth toallocate to UE 115-a for carrying a reference signal and an uplink ordownlink data transmission. In some examples, the resource blockallocation 210 may include a small number of resource blocks, forexample including two, three, or four resource blocks, or any number ofresource blocks less than or equal to a threshold number of resourceblocks (e.g., that satisfies a resource block threshold). In someexamples, the techniques described herein may be used for small lengthπ/2 BPSK DMRS sequence.

In some cases, UE 115-a may transmit or receive a reference signal 215and a data transmission 220 within resource block allocation 210, wherethe reference signal 215 may be communicated using a first subset of theresource elements of the resource block allocation 210 and the datatransmission 220 may be communicated using a second subset of theresource elements of the resource block allocation 210. The referencesignal 215 may be used to generate a channel estimate to enable areceiver to correct amplitude and/or phase distortion of the datatransmission 220 caused by the wireless channel.

For an uplink data transmission, UE 115-a may transmit, to the basestation 105-a, a reference signal 215 and the uplink data transmissionwithin resource block allocation 210, where the reference signal 215 maybe communicated using a first subset of the resource elements of theresource block allocation 210 and the uplink data transmission may becommunicated using a second subset of the resource elements of theresource block allocation 210.

For a downlink data transmission, UE 115-a may receive, from the basestation 105-a, a reference signal 215 and the downlink data transmissionwithin resource block allocation 210, where the reference signal 215 maybe communicated using a first subset of the resource elements of theresource block allocation 210 and the downlink data transmission may becommunicated using a second subset of the resource elements of theresource block allocation 210.

Base station 105-a may transmit, to UE 115-a, a grant indicating theresource block allocation 210. A grant may identify which resourceblocks within the available system bandwidth are allocated to UE 115-afor an uplink and/or downlink data transmission. In some examples, thegrant may indicate a bit sequence length of a bit sequence used togenerate the reference signal 215. In another example, UE 115-a maydetermine a length of the bit sequence based on the number of allocatedresource blocks.

In cases where the reference signal 215 is based on a ZC sequencetransmitted at a same power as data transmission 220, the base station105-a may indicate to the UE 115-a, and to other UEs 115 within thecoverage area of the base station 105-a, that a first type of referencesignal is to be transmitted for π/2 BPSK transmissions. In some cases,the UE 115-a may transmit a capability indication that indicates whetherthe UE 115-a is capable of using other types of reference signals, suchas a π/2 BPSK DMRS or a power deboosted reference signal based on a ZCsequence. Based on the capability indication, the base station 105-a mayindicate to the UE 115-a that the first type of reference signal or thesecond type of reference signal is to be transmitted. If the UE 115-a issignaled (e.g., via a modulation and coding scheme (MCS) indication in adownlink control information (DCI) transmission) that a resourceallocation is associated with π/2 BPSK transmissions, the UE 115-a maythen generate the reference signal 215 according to the indicated firsttype of reference signal or second type of reference signal.

In some examples, the second type of reference signal may be based on aπ/2 BPSK DMRS sequence. In other examples, the second type of referencesignal may be based on a same ZC sequence of the first type of referencesignal, but the transmission power of the reference signal 215 may bedeboosted by X dB (e.g., X=1, where the value of X may also be indicatedwith the indication of the second type of reference signal) with respectto data transmissions 220.

In some cases, as described above, the base station 105-a may use RRCsignaling to indicate to the UE 115-a whether the first type ofreference signal or the second type of reference signal is to be usedfor shared channel transmissions (e.g., PUSCH transmissions). Such RRCsignaling may be, in some cases, a cell -specific RRC transmission suchas SIB transmissions or either of an OSI or RMSI transmission. Forexample, the base station 105-a may use a SIB, OSI, or RMSI transmissionto indicate to UE 115-a (and all other UEs 115 served by the basestation 105-a) that the first type of reference signal is to be used. Insuch cases, even though the UE 115-a may be capable of using the secondtype of reference signal, the UE 115-a may use the first type ofreference signal for π/2 BPSK transmissions. In some cases, if one ormore UEs 115 served by the base station 105-a are not capable of usingthe second type of reference signal, the base station 105-a may signalto all served UEs 115 to use the first type of reference signal. Inother cases, after the UE 115-a reports its capability, the base station105-a may use UE -specific RRC to indicate that the second type ofreference signal is to be used by the UE 115-a. In such UE-specificsignaling cases, the base station 105-a may configure some UEs 115 touse the first type of reference signal and other UEs 115 to use thesecond type of reference signal. In some cases, if the UE 115-a iscapable of using the first type of reference signal (e.g., and notcapable of using the second type of reference signal), the base station105-a may not send any RRC signaling that indicates a type of referencesignal, such that the UE 115-a may use the first type of referencesignal.

In some cases, cell-specific RRC may be used to establish an initialtype of reference signal (e.g., the first type of reference signal) thatis to be used by UE 115-a and, after the UE 115-a reports a capabilityfor different types of reference signals (e.g., via a PUSCHtransmission), the base station 105-a may transmit UE-specific RRCsignaling that indicates which type of reference signal to use for oneor more subsequent transmissions (e.g., an RRC reconfiguration mayindicate which type of reference signal is to be used, a SPS grant mayindicate a type of reference signal to use for SPS transmissions, etc.).If the indication from the UE-specific RRC is different than the initialtype of reference signal, the indication from the UE-specific RRC mayoverride the initial type of reference signal.

FIG. 3 illustrates an example of a wireless communications system 300that supports reference signal sequence identification in wirelesscommunications in accordance with aspects of the present disclosure. Insome examples, wireless communications system 300 may implement aspectsof wireless communications system 100. In this example, wirelesscommunications system 300 includes a first UE 115-b, a second UE 115-b,and a base station 105-b, which may be respective examples of a UE 115and a base station 105 as described herein. First UE 115-b and basestation 105-b may communicate via a communication link 305 and second UE115-c and base station 105-b may communicate via a communication link310. Similarly as discussed with respect to FIG. 2, communication links305 and 310 may be configured for uplink and downlink transmission.

In this example, the base station 105-b may use UE-specific RRCsignaling to indicate a first type of reference signal and a second typeof reference signal that is to be used by UEs 115-b and 115-c for π/2BPSK transmissions. In this case, communication link 305 with the firstUE 115-b may use a first type of reference signal 315, which may have ahigher PAPR relative to data transmissions 320 of resource blockallocation 210-a. Communication link 310 with the second UE 115-c mayuse a second type of reference signal 325, which may have a similar orlower PAPR as data transmissions 320 of resource block allocation 210-b.In some examples, UEs 115-b and 115-c and base station 105-b may use π/2BPSK modulation and the base station 105-b may signal a reference signalthat the UE 115-c is to use for π/2 BPSK transmissions. As indicatedabove, in some cases the second UE 115-c may transmit a capabilityindication to the base station 105-b, indicating a capability withreference to the second type of reference signal 325, and the basestation 105-b may provide an indication via RRC signaling that thesecond UE 115-c is to use the first type of reference signal or thesecond type of reference signal. Also, as indicated above, in some casesthe base station 105-b may provide an initial indication to the secondUE 115-c that the first type of reference signal 315 is to be used and,upon receiving capability information that the second UE 115-c iscapable of using the second type of reference signal 325, may transmitUE-specific signaling to the second UE 115-c, indicating for the UE115-c to use the second type of reference signal 325.

As discussed above, in some cases the base station 105-b may transmit anindication to use a second type of reference signal 325. Such referencesignals may provide lower power transmissions, or lower PAPR. In somecases, the second reference signal 325 may be a power deboosted versionof the first reference signal 315. In other cases, the second referencesignal 325 may be π/2 BPSK DMRS in which a length of a bit sequence ofthe second reference signal 325 may correspond to a number of allocatedresource blocks within which data and the reference signal are to betransmitted. In such examples, base station 105-b and second UE 115-cmay each store a set of tables that each includes sets of bit sequencesthat may be used to generate the second reference signal 325, and thesecond reference signal 325 may be generated based on a table of the setof tables that corresponds to the resource block allocation 210-b.

FIG. 4 illustrates an example of a process flow 400 that supportsreference signal sequence identification in wireless communications inaccordance with aspects of the present disclosure. In some examples,process flow 400 may implement aspects of wireless communications system100, 200, or 300. Process flow 400 may include UE 115-d and base station105-c, which may be respective examples of a UE 115 and a base station105 as described herein. Process flow 400 may implement techniques forsignaling an uplink reference signal using π/2 BPSK modulation.

At 405, UE 115-d and base station 105-c may establish communications(e.g., establish a connection). In some cases, during connectionestablishment (e.g., RRC connection establishment or RRC connectionreconfiguration), base station 105-c may semi-statically configure UE115-d with a type of reference signal for use in π/2 BPSK modulationcommunications. In some cases, an initial type of reference signal maybe configured via cell-specific RRC signaling.

At 410, UE 115-d may, in some cases, transmit a capability indication tothe base station 105-c that may indicate whether the UE 115-d is capableof using different types of reference signals for π/2 BPSKtransmissions. In some cases, the capability indication may be providedvia RRC signaling as part of the connection establishment. In somecases, the base station 105-c may transmit a separate capability requestto the UE 115-d, and the capability indication may be providedresponsive to the capability request (e.g., via PUSCH). The capabilityindication may be an explicit indication provided by the UE 115-d, ormay be an implicit indication based on one or more other capabilities ofthe UE 115-d (e.g., a capability of the UE 115-d to perform one or moreadvanced features, such as those associated with a newer release of aradio communications standard).

At 415, the base station 105-c may transmit a reference signal typeindication to the UE 115-d. In some cases, the reference signal typeindication may indicate whether the UE 115-d is to use a first type ofreference signal or a second type of reference signal. The first type ofreference signal may be based on a ZC sequence and may be transmitted ata same power level as data transmissions. In some cases, The second typeof reference signal may be a power deboosted reference signal that isbased on the ZC sequence that is transmitted at a lower power level thanthe data transmissions. In such cases, the reference signal typeindication may also indicate an amount of power deboosting that is to beused (e.g., a 1 dB power reduction for DMRS transmissions). In somecases, the second type of reference signal may be based on a π/2 BPSKDMRS sequence that has a lower PAPR than the ZC sequence, which may havea similar PAPR to data transmissions within a resource allocation.

At 420, base station 105-c may determine a DMRS sequence for π/2 BPSKmodulation transmissions. In some cases, as discussed above, the basestation 105-c may determine to use a power deboosted version of areference signal based on a ZC sequence, and the DMRS sequence may bethe power deboosted version of ZC sequence. In other cases, the basestation 105-c may determine a bit sequence length corresponding to thenumber of allocated resource blocks, identify a bit sequence table fromthe set of bit sequence tables based on the determined bit sequencelength, and select a bit sequence from a set of bit sequences in theidentified bit sequence table.

At 425, base station 105-c may transmit control information to UE 115-dindicating the number of allocated resource blocks. In some cases, thecontrol information may indicate a type of reference signal to be usedfor DMRS transmissions of the UE 115-d. In an example, the controlinformation may include a grant allocating a set of resource blocks tothe UE 115-d for transmitting a reference signal and an uplink datatransmission to the base station 105-c. In some cases, the controlinformation may include the index value for the identified bit sequencetable to indicate which bit sequence of the set of bit sequences to usefrom the bit sequence table for the π/2 BPSK DMRS sequence. In somecases, base station 105-c may signal the bit sequence length to UE 115-d(e.g., in the grant or other DCI), or UE 115-d may determine the bitsequence length based on the number of allocated resource blocks (e.g.,a bit sequence length may be a function of the number of allocatedresource blocks).

At 430, UE 115-d may determine the DMRS sequence. In cases where thebase station 105-c indicates that a power deboosted reference signal isto be transmitted, the UE may determine the DMRS sequence based on a ZCsequence. In cases where the base station 105-c indicates that a π/2BPSK DMRS sequence is to be used, the UE 115-d may identify a π/2 BPSKDMRS sequence. In some cases, the UE 115-d may identify the π/2 BPSKDMRS sequence based on a resource block allocation and an index valueprovided with the control information. In an example, the UE 115-d mayprocess the control information to identify the set of allocatedresource blocks and the number of allocated resource blocks and UE 115-dmay determine the bit sequence length corresponding to the number ofallocated resource blocks.

At 435, UE 115-d may generate the reference signal. In some cases, thereference signal may be generated by modulating the identified referencesignal sequence according to a π/2 BPSK modulation scheme. In caseswhere the base station 105-c provides an initial type of referencesignal, if the reference signal type indication is different than theinitial type reference signal, the UE 115-d may switch the type ofreference signal in accordance with the reference signal typeindication.

At 440, UE 115-d may transmit the reference signal and the uplink datatransmission to base station 105-c within the allocated resource blocks.The reference signal may be, for example a DMRS. In cases where thesecond type of reference signal is π/2 BPSK DMRS, a PAPR of tones of theuplink data transmission transporting the modulated data bit sequencewithin the allocated resource blocks may satisfy a PAPR threshold, and aPAPR of tones transporting the reference signal within the allocatedresource blocks may have a similar or lower PAPR. Therefore, thereference signal and data may use a same modulation scheme resulting ina low PAPR for both the reference signal and the uplink datatransmission.

At 445, base station 105-c may monitor the allocated resource blocks forthe reference signal and the uplink data transmission. Base station105-c may receive the reference signal within the allocated resourceblocks for estimating amplitude and/or phase distortion introduced tothe uplink data transmission by the wireless channel. Base station 105-cmay remove the amplitude and/or phase distortion during decoding of theuplink data transmission based on the received reference signal. In somecases, the wireless channel may introduce delay to the reference signal,and each bit sequence used to generate the reference signal may beorthogonal to at least one delayed version of the same bit sequence todistinguish multipath interference.

FIG. 5 shows a block diagram 500 of a device 505 that supports referencesignal sequence identification in wireless communications in accordancewith aspects of the present disclosure. The device 505 may be an exampleof aspects of a UE 115 as described herein. The device 505 may include areceiver 510, a communications manager 515, and a transmitter 520. Thedevice 505 may also include a processor. Each of these components may bein communication with one another (e.g., via one or more buses).

The receiver 510 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to referencesignal sequence identification in wireless communications, etc.).Information may be passed on to other components of the device 505. Thereceiver 510 may be an example of aspects of the transceiver 820described with reference to FIG. 8. The receiver 510 may utilize asingle antenna or a set of antennas.

The communications manager 515 may establish a connection with a basestation that uses a π/2 BPSK modulation scheme for at least a portion ofwireless communications with the base station, receive, from the basestation, an indication of a type of reference signal sequence to beincluded within transmissions that use the π/2 BPSK modulation scheme,generate a reference signal based on the indication of the type ofreference signal sequence, and transmit the reference signal withincommunications that use the π/2 BPSK modulation scheme. Thecommunications manager 515 may be an example of aspects of thecommunications manager 810 described herein.

The communications manager 515, or its sub-components, may beimplemented in hardware, code (e.g., software or firmware) executed by aprocessor, or any combination thereof. If implemented in code executedby a processor, the functions of the communications manager 515, or itssub-components may be executed by a general-purpose processor, a digitalsignal processor (DSP), an application-specific integrated circuit(ASIC), a field-programmable gate array (FPGA) or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed in the present disclosure.

The communications manager 515, or its sub-components, may be physicallylocated at various positions, including being distributed such thatportions of functions are implemented at different physical locations byone or more physical components. In some examples, the communicationsmanager 515, or its sub-components, may be a separate and distinctcomponent in accordance with various aspects of the present disclosure.In some examples, the communications manager 515, or its sub-components,may be combined with one or more other hardware components, includingbut not limited to an input/output (I/O) component, a transceiver, anetwork server, another computing device, one or more other componentsdescribed in the present disclosure, or a combination thereof inaccordance with various aspects of the present disclosure.

The transmitter 520 may transmit signals generated by other componentsof the device 505. In some examples, the transmitter 520 may becollocated with a receiver 510 in a transceiver module. For example, thetransmitter 520 may be an example of aspects of the transceiver 820described with reference to FIG. 8. The transmitter 520 may utilize asingle antenna or a set of antennas.

FIG. 6 shows a block diagram 600 of a device 605 that supports referencesignal sequence identification in wireless communications in accordancewith aspects of the present disclosure. The device 605 may be an exampleof aspects of a device 505 or a UE 115 as described herein. The device605 may include a receiver 610, a communications manager 615, and atransmitter 635. The device 605 may also include a processor. Each ofthese components may be in communication with one another (e.g., via oneor more buses).

The receiver 610 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to referencesignal sequence identification in wireless communications, etc.).Information may be passed on to other components of the device 605. Thereceiver 610 may be an example of aspects of the transceiver 820described with reference to FIG. 8. The receiver 610 may utilize asingle antenna or a set of antennas.

The communications manager 615 may be an example of aspects of thecommunications manager 515 as described herein. The communicationsmanager 615 may include a connection establishment component 620, areference signal component 625, and a π/2 BPSK modulation component 630.The communications manager 615 may be an example of aspects of thecommunications manager 810 described herein.

The connection establishment component 620 may establish a connectionwith a base station that uses a π/2 BPSK modulation scheme for at leasta portion of wireless communications with the base station.

The reference signal component 625 may receive, from the base station,an indication of a type of reference signal sequence to be includedwithin transmissions that use the π/2 BPSK modulation scheme andgenerate a reference signal based on the indication of the type ofreference signal sequence.

The π/2 BPSK modulation component 630 may transmit the reference signalwithin communications that use the π/2 BPSK modulation scheme.

The transmitter 635 may transmit signals generated by other componentsof the device 605. In some examples, the transmitter 635 may becollocated with a receiver 610 in a transceiver module. For example, thetransmitter 635 may be an example of aspects of the transceiver 820described with reference to FIG. 8. The transmitter 635 may utilize asingle antenna or a set of antennas.

FIG. 7 shows a block diagram 700 of a communications manager 705 thatsupports reference signal sequence identification in wirelesscommunications in accordance with aspects of the present disclosure. Thecommunications manager 705 may be an example of aspects of acommunications manager 515, a communications manager 615, or acommunications manager 810 described herein. The communications manager705 may include a connection establishment component 710, a referencesignal component 715, a π/2 BPSK modulation component 720, a sequencegeneration component 725, an RRC component 730, a capability indicationcomponent 735, and a resource allocation component 740. Each of thesemodules may communicate, directly or indirectly, with one another (e.g.,via one or more buses).

The connection establishment component 710 may establish a connectionwith a base station that uses a π/2 BPSK modulation scheme for at leasta portion of wireless communications with the base station.

The reference signal component 715 may receive, from the base station,an indication of a type of reference signal sequence to be includedwithin transmissions that use the π/2 BPSK modulation scheme. In someexamples, the reference signal component 715 may generate a referencesignal based on the indication of the type of reference signal sequence.In some examples, the reference signal component 715 may determine a bitsequence length for the reference signal corresponding to the number ofallocated resource blocks. In some examples, the reference signalcomponent 715 may generate the reference signal based on a bit sequencehaving the bit sequence length.

In some cases, the indication of the type of reference signal sequenceindicates a first type of reference signal sequence or a second type ofreference signal sequence. In some cases, the second type of referencesignal sequence has a lower PAPR than the first type of reference signalsequence. In some cases, the second type of reference signal sequence isa power deboosted version of the first sequence. In some cases, theindication of the type of reference signal sequence indicates the powerdeboosted ZC sequence and an amount of power deboosting to applyrelative to data transmissions that use the π/2 BPSK modulation scheme.

The π/2 BPSK modulation component 720 may transmit the reference signalwithin communications that use the π/2 BPSK modulation scheme.

The sequence generation component 725 may generate a reference signalsequence. In some cases, the first type of reference signal sequence isa ZC sequence. In some cases, the second type of reference signalsequence is a power deboosted ZC sequence. In other cases, the secondtype of reference signal sequence is a π/2 BPSK DMRS sequence.

The RRC component 730 may transmit and receive RRC signaling from a basestation. In some cases, the indication of a type of reference signal touse for π/2 BPSK DMRS transmissions is received via RRC signaling. Insome cases, the RRC signaling is a cell-specific RRC transmission thatindicates the type of reference signal sequence to be used by each UE ina cell served by the base station. In some cases, the cell-specific RRCtransmission includes a SIB transmission or either an OSI or RMSItransmission from the base station. In some cases, the RRC signaling isa UE-specific RRC transmission that indicates the type of referencesignal sequence to be used by the UE.

The capability indication component 735 may transmit a capabilityindication to the base station that indicates supported types ofreference signals at the UE, and where the indication of the type ofreference signal is received responsive to the capability indication.

The resource allocation component 740 may identify a set of allocatedresource blocks and a number of the allocated resource blocks for atleast a first transmission using the π/2 BPSK modulation scheme.

FIG. 8 shows a diagram of a system 800 including a device 805 thatsupports reference signal sequence identification in wirelesscommunications in accordance with aspects of the present disclosure. Thedevice 805 may be an example of or include the components of device 505,device 605, or a UE 115 as described herein. The device 805 may includecomponents for bi-directional voice and data communications includingcomponents for transmitting and receiving communications, including acommunications manager 810, an I/O controller 815, a transceiver 820, anantenna 825, memory 830, and a processor 840. These components may be inelectronic communication via one or more buses (e.g., bus 845).

The communications manager 810 may establish a connection with a basestation that uses a π/2 BPSK modulation scheme for at least a portion ofwireless communications with the base station, receive, from the basestation, an indication of a type of reference signal sequence to beincluded within transmissions that use the π/2 BPSK modulation scheme,generate a reference signal based on the indication of the type ofreference signal sequence, and transmit the reference signal withincommunications that use the π/2 BPSK modulation scheme.

The I/O controller 815 may manage input and output signals for thedevice 805. The I/O controller 815 may also manage peripherals notintegrated into the device 805. In some cases, the I/O controller 815may represent a physical connection or port to an external peripheral.In some cases, the I/O controller 815 may utilize an operating systemsuch as iOS®, ANDROID®, MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, oranother known operating system. In other cases, the I/O controller 815may represent or interact with a modem, a keyboard, a mouse, atouchscreen, or a similar device. In some cases, the I/O controller 815may be implemented as part of a processor. In some cases, a user mayinteract with the device 805 via the I/O controller 815 or via hardwarecomponents controlled by the I/O controller 815.

The transceiver 820 may communicate bi-directionally, via one or moreantennas, wired, or wireless links as described above. For example, thetransceiver 820 may represent a wireless transceiver and may communicatebi-directionally with another wireless transceiver. The transceiver 820may also include a modem to modulate the packets and provide themodulated packets to the antennas for transmission, and to demodulatepackets received from the antennas.

In some cases, the wireless device may include a single antenna 825.However, in some cases the device may have more than one antenna 825,which may be capable of concurrently transmitting or receiving multiplewireless transmissions.

The memory 830 may include random access memory (RAM) and read onlymemory (ROM). The memory 830 may store computer-readable,computer-executable code 835 including instructions that, when executed,cause the processor to perform various functions described herein. Insome cases, the memory 830 may contain, among other things, a basic I/Osystem (BIOS) which may control basic hardware or software operationsuch as the interaction with peripheral components or devices.

The processor 840 may include an intelligent hardware device, (e.g., ageneral-purpose processor, a DSP, a central processing unit (CPU), amicrocontroller, an ASIC, an FPGA, a programmable logic device, adiscrete gate or transistor logic component, a discrete hardwarecomponent, or any combination thereof). In some cases, the processor 840may be configured to operate a memory array using a memory controller.In other cases, a memory controller may be integrated into the processor840. The processor 840 may be configured to execute computer-readableinstructions stored in a memory (e.g., the memory 830) to cause thedevice 805 to perform various functions (e.g., functions or taskssupporting reference signal sequence identification in wirelesscommunications).

The code 835 may include instructions to implement aspects of thepresent disclosure, including instructions to support wirelesscommunications. The code 835 may be stored in a non-transitorycomputer-readable medium such as system memory or other type of memory.In some cases, the code 835 may not be directly executable by theprocessor 840 but may cause a computer (e.g., when compiled andexecuted) to perform functions described herein.

FIG. 9 shows a block diagram 900 of a device 905 that supports referencesignal sequence identification in wireless communications in accordancewith aspects of the present disclosure. The device 905 may be an exampleof aspects of a base station 105 as described herein. The device 905 mayinclude a receiver 910, a communications manager 915, and a transmitter920. The device 905 may also include a processor. Each of thesecomponents may be in communication with one another (e.g., via one ormore buses).

The receiver 910 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to referencesignal sequence identification in wireless communications, etc.).Information may be passed on to other components of the device 905. Thereceiver 910 may be an example of aspects of the transceiver 1220described with reference to FIG. 12. The receiver 910 may utilize asingle antenna or a set of antennas.

The communications manager 915 may establish a connection with at leasta first UE that uses a π/2 BPSK modulation scheme for at least a portionof wireless communications with the first UE, transmit an indication ofa type of reference signal sequence to be included within transmissionsof at least the first UE that use the π/2 BPSK modulation scheme,receive a transmission from at least the first UE that uses the π/2 BPSKmodulation scheme and that includes a reference signal based on theindication of the type of reference signal sequence, and demodulate thetransmission based on the reference signal. The communications manager915 may be an example of aspects of the communications manager 1210described herein.

The communications manager 915, or its sub-components, may beimplemented in hardware, code (e.g., software or firmware) executed by aprocessor, or any combination thereof. If implemented in code executedby a processor, the functions of the communications manager 915, or itssub-components may be executed by a general-purpose processor, a DSP, anASIC, a FPGA or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described in the presentdisclosure.

The communications manager 915, or its sub-components, may be physicallylocated at various positions, including being distributed such thatportions of functions are implemented at different physical locations byone or more physical components. In some examples, the communicationsmanager 915, or its sub-components, may be a separate and distinctcomponent in accordance with various aspects of the present disclosure.In some examples, the communications manager 915, or its sub-components,may be combined with one or more other hardware components, includingbut not limited to an I/O component, a transceiver, a network server,another computing device, one or more other components described in thepresent disclosure, or a combination thereof in accordance with variousaspects of the present disclosure.

The transmitter 920 may transmit signals generated by other componentsof the device 905. In some examples, the transmitter 920 may becollocated with a receiver 910 in a transceiver module. For example, thetransmitter 920 may be an example of aspects of the transceiver 1220described with reference to FIG. 12. The transmitter 920 may utilize asingle antenna or a set of antennas.

FIG. 10 shows a block diagram 1000 of a device 1005 that supportsreference signal sequence identification in wireless communications inaccordance with aspects of the present disclosure. The device 1005 maybe an example of aspects of a device 905 or a base station 105 asdescribed herein. The device 1005 may include a receiver 1010, acommunications manager 1015, and a transmitter 1035. The device 1005 mayalso include a processor. Each of these components may be incommunication with one another (e.g., via one or more buses).

The receiver 1010 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to referencesignal sequence identification in wireless communications, etc.).Information may be passed on to other components of the device 1005. Thereceiver 1010 may be an example of aspects of the transceiver 1220described with reference to FIG. 12. The receiver 1010 may utilize asingle antenna or a set of antennas.

The communications manager 1015 may be an example of aspects of thecommunications manager 915 as described herein. The communicationsmanager 1015 may include a connection establishment component 1020, areference signal component 1025, and a π/2 BPSK modulation component1030. The communications manager 1015 may be an example of aspects ofthe communications manager 1210 described herein.

The connection establishment component 1020 may establish a connectionwith at least a first UE that uses a π/2 BPSK modulation scheme for atleast a portion of wireless communications with the first UE.

The reference signal component 1025 may transmit an indication of a typeof reference signal sequence to be included within transmissions of atleast the first UE that use the π/2 BPSK modulation scheme and receive atransmission from at least the first UE that uses the π/2 BPSKmodulation scheme and that includes a reference signal based on theindication of the type of reference signal sequence.

The π/2 BPSK modulation component 1030 may demodulate the transmissionbased on the reference signal.

The transmitter 1035 may transmit signals generated by other componentsof the device 1005. In some examples, the transmitter 1035 may becollocated with a receiver 1010 in a transceiver module. For example,the transmitter 1035 may be an example of aspects of the transceiver1220 described with reference to FIG. 12. The transmitter 1035 mayutilize a single antenna or a set of antennas.

FIG. 11 shows a block diagram 1100 of a communications manager 1105 thatsupports reference signal sequence identification in wirelesscommunications in accordance with aspects of the present disclosure. Thecommunications manager 1105 may be an example of aspects of acommunications manager 915, a communications manager 1015, or acommunications manager 1210 described herein. The communications manager1105 may include a connection establishment component 1110, a referencesignal component 1115, a π/2 BPSK modulation component 1120, an RRCcomponent 1125, and a capability indication component 1130. Each ofthese modules may communicate, directly or indirectly, with one another(e.g., via one or more buses).

The connection establishment component 1110 may establish a connectionwith at least a first UE that uses a π/2 BPSK modulation scheme for atleast a portion of wireless communications with the first UE.

The reference signal component 1115 may transmit an indication of a typeof reference signal sequence to be included within transmissions of atleast the first UE that use the π/2 BPSK modulation scheme. In someexamples, the reference signal component 1115 may receive a transmissionfrom at least the first UE that uses the π/2 BPSK modulation scheme andthat includes a reference signal based on the indication of the type ofreference signal sequence.

In some cases, the indication of the type of reference signal sequenceindicates a first type of reference signal sequence or a second type ofreference signal sequence. In some cases, the second type of referencesignal sequence has a lower PAPR than the first type of referencesignal. In some cases, the second type of reference signal sequence is apower deboosted version of the first sequence. In some cases, the firsttype of reference signal sequence is a ZC sequence. In some cases, thesecond type of reference signal sequence is a power deboosted ZCsequence or a π/2 BPSK DMRS sequence. In some cases, the indication ofthe type of reference signal sequence indicates the power deboosted ZCsequence and an amount of power deboosting to apply relative to datatransmissions that use the π/2 BPSK modulation scheme.

The π/2 BPSK modulation component 1120 may demodulate the transmissionbased on the reference signal.

The RRC component 1125 may transmit and receive RRC signaling. In somecases, the indication of the type of reference signal sequence istransmitted via RRC signaling. In some cases, the RRC signaling is acell-specific RRC transmission that indicates the type of referencesignal sequence to be used by each UE in a cell served by the basestation. In some cases, the cell-specific RRC transmission includes aSIB transmission, an OSI transmission, or an RMSI transmission. In somecases, the RRC signaling is a UE-specific RRC transmission thatindicates the type of reference signal sequence to be used by the firstUE, and where one or more other UEs use a different type of referencesignal sequence for transmissions that use the π/2 BPSK modulationscheme.

The capability indication component 1130 may receive, from the first UE,a capability indication that indicates supported types of referencesignals at the UE, and where the indication of the type of referencesignal sequence is transmitted to the first UE responsive to thecapability indication.

FIG. 12 shows a diagram of a system 1200 including a device 1205 thatsupports reference signal sequence identification in wirelesscommunications in accordance with aspects of the present disclosure. Thedevice 1205 may be an example of or include the components of device905, device 1005, or a base station 105 as described herein. The device1205 may include components for bi-directional voice and datacommunications including components for transmitting and receivingcommunications, including a communications manager 1210, a networkcommunications manager 1215, a transceiver 1220, an antenna 1225, memory1230, a processor 1240, and an inter-station communications manager1245. These components may be in electronic communication via one ormore buses (e.g., bus 1250).

The communications manager 1210 may establish a connection with at leasta first UE that uses a π/2 BPSK modulation scheme for at least a portionof wireless communications with the first UE, transmit an indication ofa type of reference signal sequence to be included within transmissionsof at least the first UE that use the π/2 BPSK modulation scheme,receive a transmission from at least the first UE that uses the π/2 BPSKmodulation scheme and that includes a reference signal based on theindication of the type of reference signal sequence, and demodulate thetransmission based on the reference signal.

The network communications manager 1215 may manage communications withthe core network (e.g., via one or more wired backhaul links). Forexample, the network communications manager 1215 may manage the transferof data communications for client devices, such as one or more UEs 115.

The transceiver 1220 may communicate bi-directionally, via one or moreantennas, wired, or wireless links as described above. For example, thetransceiver 1220 may represent a wireless transceiver and maycommunicate bi-directionally with another wireless transceiver. Thetransceiver 1220 may also include a modem to modulate the packets andprovide the modulated packets to the antennas for transmission, and todemodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1225.However, in some cases the device may have more than one antenna 1225,which may be capable of concurrently transmitting or receiving multiplewireless transmissions.

The memory 1230 may include RAM, ROM, or a combination thereof. Thememory 1230 may store computer-readable code 1235 including instructionsthat, when executed by a processor (e.g., the processor 1240) cause thedevice to perform various functions described herein. In some cases, thememory 1230 may contain, among other things, a BIOS which may controlbasic hardware or software operation such as the interaction withperipheral components or devices.

The processor 1240 may include an intelligent hardware device, (e.g., ageneral-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, anFPGA, a programmable logic device, a discrete gate or transistor logiccomponent, a discrete hardware component, or any combination thereof).In some cases, the processor 1240 may be configured to operate a memoryarray using a memory controller. In some cases, a memory controller maybe integrated into processor 1240. The processor 1240 may be configuredto execute computer-readable instructions stored in a memory (e.g., thememory 1230) to cause the device to perform various functions (e.g.,functions or tasks supporting reference signal sequence identificationin wireless communications).

The inter-station communications manager 1245 may manage communicationswith other base station 105, and may include a controller or schedulerfor controlling communications with UEs 115 in cooperation with otherbase stations 105. For example, the inter-station communications manager1245 may coordinate scheduling for transmissions to UEs 115 for variousinterference mitigation techniques such as beamforming or jointtransmission. In some examples, the inter-station communications manager1245 may provide an X2 interface within an LTE/LTE-A wirelesscommunication network technology to provide communication between basestations 105.

The code 1235 may include instructions to implement aspects of thepresent disclosure, including instructions to support wirelesscommunications. The code 1235 may be stored in a non-transitorycomputer-readable medium such as system memory or other type of memory.In some cases, the code 1235 may not be directly executable by theprocessor 1240 but may cause a computer (e.g., when compiled andexecuted) to perform functions described herein.

FIG. 13 shows a flowchart illustrating a method 1300 that supportsreference signal sequence identification in wireless communications inaccordance with aspects of the present disclosure. The operations ofmethod 1300 may be implemented by a UE 115 or its components asdescribed herein. For example, the operations of method 1300 may beperformed by a communications manager as described with reference toFIGS. 5 through 8. In some examples, a UE may execute a set ofinstructions to control the functional elements of the UE to perform thefunctions described below. Additionally or alternatively, a UE mayperform aspects of the functions described below using special-purposehardware.

At 1305, the UE may establish a connection with a base station that usesa π/2 BPSK modulation scheme for at least a portion of wirelesscommunications with the base station. The operations of 1305 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1305 may be performed by a connectionestablishment component as described with reference to FIGS. 5 through8.

At 1310, the UE may receive, from the base station, an indication of atype of reference signal sequence to be included within transmissionsthat use the π/2 BPSK modulation scheme. The operations of 1310 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1310 may be performed by a reference signalcomponent as described with reference to FIGS. 5 through 8.

At 1315, the UE may generate a reference signal based on the indicationof the type of reference signal sequence. The operations of 1315 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1315 may be performed by a reference signalcomponent as described with reference to FIGS. 5 through 8.

At 1320, the UE may transmit the reference signal within communicationsthat use the π/2 BPSK modulation scheme. The operations of 1320 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1320 may be performed by a π/2 BPSKmodulation component as described with reference to FIGS. 5 through 8.

FIG. 14 shows a flowchart illustrating a method 1400 that supportsreference signal sequence identification in wireless communications inaccordance with aspects of the present disclosure. The operations ofmethod 1400 may be implemented by a UE 115 or its components asdescribed herein. For example, the operations of method 1400 may beperformed by a communications manager as described with reference toFIGS. 5 through 8. In some examples, a UE may execute a set ofinstructions to control the functional elements of the UE to perform thefunctions described below. Additionally or alternatively, a UE mayperform aspects of the functions described below using special-purposehardware.

At 1405, the UE may establish a connection with a base station that usesa π/2 BPSK modulation scheme for at least a portion of wirelesscommunications with the base station. The operations of 1405 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1405 may be performed by a connectionestablishment component as described with reference to FIGS. 5 through8.

At 1410, the UE may transmit a capability indication to the base stationthat indicates supported types of reference signals at the UE. Theoperations of 1410 may be performed according to the methods describedherein. In some examples, aspects of the operations of 1410 may beperformed by a capability indication component as described withreference to FIGS. 5 through 8.

At 1415, the UE may receive, from the base station, an indication of atype of reference signal sequence to be included within transmissionsthat use the π/2 BPSK modulation scheme. The operations of 1415 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1415 may be performed by a reference signalcomponent as described with reference to FIGS. 5 through 8. In somecases, the indication of the type of reference signal is responsive tothe capability indication transmitted by the UE.

At 1420, the UE may generate a reference signal based on the indicationof the type of reference signal sequence. The operations of 1420 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1420 may be performed by a reference signalcomponent as described with reference to FIGS. 5 through 8.

At 1425, the UE may transmit the reference signal within communicationsthat use the π/2 BPSK modulation scheme. The operations of 1425 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1425 may be performed by a π/2 BPSKmodulation component as described with reference to FIGS. 5 through 8.

FIG. 15 shows a flowchart illustrating a method 1500 that supportsreference signal sequence identification in wireless communications inaccordance with aspects of the present disclosure. The operations ofmethod 1500 may be implemented by a UE 115 or its components asdescribed herein. For example, the operations of method 1500 may beperformed by a communications manager as described with reference toFIGS. 5 through 8. In some examples, a UE may execute a set ofinstructions to control the functional elements of the UE to perform thefunctions described below. Additionally or alternatively, a UE mayperform aspects of the functions described below using special-purposehardware.

At 1505, the UE may establish a connection with a base station that usesa π/2 BPSK modulation scheme for at least a portion of wirelesscommunications with the base station. The operations of 1505 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1505 may be performed by a connectionestablishment component as described with reference to FIGS. 5 through8.

At 1510, the UE may receive, from the base station, an indication of atype of reference signal sequence to be included within transmissionsthat use the π/2 BPSK modulation scheme. The operations of 1510 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1510 may be performed by a reference signalcomponent as described with reference to FIGS. 5 through 8.

At 1515, the UE may identify a set of allocated resource blocks and anumber of the allocated resource blocks for at least a firsttransmission using the π/2 BPSK modulation scheme. The operations of1515 may be performed according to the methods described herein. In someexamples, aspects of the operations of 1515 may be performed by aresource allocation component as described with reference to FIGS. 5through 8.

At 1520, the UE may determine a bit sequence length for the referencesignal corresponding to the number of allocated resource blocks. Theoperations of 1520 may be performed according to the methods describedherein. In some examples, aspects of the operations of 1520 may beperformed by a reference signal component as described with reference toFIGS. 5 through 8.

At 1525, the UE may generate the reference signal based on a bitsequence having the bit sequence length. The operations of 1525 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1525 may be performed by a reference signalcomponent as described with reference to FIGS. 5 through 8.

At 1530, the UE may transmit the reference signal within communicationsthat use the π/2 BPSK modulation scheme. The operations of 1530 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1530 may be performed by a π/2 BPSKmodulation component as described with reference to FIGS. 5 through 8.

FIG. 16 shows a flowchart illustrating a method 1600 that supportsreference signal sequence identification in wireless communications inaccordance with aspects of the present disclosure. The operations ofmethod 1600 may be implemented by a base station 105 or its componentsas described herein. For example, the operations of method 1600 may beperformed by a communications manager as described with reference toFIGS. 9 through 12. In some examples, a base station may execute a setof instructions to control the functional elements of the base stationto perform the functions described below. Additionally or alternatively,a base station may perform aspects of the functions described belowusing special-purpose hardware.

At 1605, the base station may establish a connection with at least afirst UE that uses a π/2 BPSK modulation scheme for at least a portionof wireless communications with the first UE. The operations of 1605 maybe performed according to the methods described herein. In someexamples, aspects of the operations of 1605 may be performed by aconnection establishment component as described with reference to FIGS.9 through 12.

At 1610, the base station may transmit an indication of a type ofreference signal sequence to be included within transmissions of atleast the first UE that use the π/2 BPSK modulation scheme. Theoperations of 1610 may be performed according to the methods describedherein. In some examples, aspects of the operations of 1610 may beperformed by a reference signal component as described with reference toFIGS. 9 through 12.

At 1615, the base station may receive a transmission from at least thefirst UE that uses the π/2 BPSK modulation scheme and that includes areference signal based on the indication of the type of reference signalsequence. The operations of 1615 may be performed according to themethods described herein. In some examples, aspects of the operations of1615 may be performed by a reference signal component as described withreference to FIGS. 9 through 12.

At 1620, the base station may demodulate the transmission based on thereference signal. The operations of 1620 may be performed according tothe methods described herein.

In some examples, aspects of the operations of 1620 may be performed bya π/2 BPSK modulation component as described with reference to FIGS. 9through 12.

FIG. 17 shows a flowchart illustrating a method 1700 that supportsreference signal sequence identification in wireless communications inaccordance with aspects of the present disclosure. The operations ofmethod 1700 may be implemented by a base station 105 or its componentsas described herein. For example, the operations of method 1700 may beperformed by a communications manager as described with reference toFIGS. 9 through 12. In some examples, a base station may execute a setof instructions to control the functional elements of the base stationto perform the functions described below. Additionally or alternatively,a base station may perform aspects of the functions described belowusing special-purpose hardware.

At 1705, the base station may establish a connection with at least afirst UE that uses a π/2 BPSK modulation scheme for at least a portionof wireless communications with the first UE. The operations of 1705 maybe performed according to the methods described herein. In someexamples, aspects of the operations of 1705 may be performed by aconnection establishment component as described with reference to FIGS.9 through 12.

At 1710, the base station may receive, from the first UE, a capabilityindication that indicates supported types of reference signals at theUE, where an indication of the type of reference signal sequence istransmitted to the first UE responsive to the capability indication. Theoperations of 1710 may be performed according to the methods describedherein. In some examples, aspects of the operations of 1710 may beperformed by a capability indication component as described withreference to FIGS. 9 through 12.

At 1715, the base station may transmit an indication of a type ofreference signal sequence to be included within transmissions of atleast the first UE that use the π/2 BPSK modulation scheme. Theoperations of 1715 may be performed according to the methods describedherein. In some examples, aspects of the operations of 1715 may beperformed by a reference signal component as described with reference toFIGS. 9 through 12.

At 1720, the base station may receive a transmission from at least thefirst UE that uses the π/2 BPSK modulation scheme and that includes areference signal based on the indication of the type of reference signalsequence. The operations of 1720 may be performed according to themethods described herein. In some examples, aspects of the operations of1720 may be performed by a reference signal component as described withreference to FIGS. 9 through 12.

At 1725, the base station may demodulate the transmission based on thereference signal. The operations of 1725 may be performed according tothe methods described herein.

In some examples, aspects of the operations of 1725 may be performed bya π/2 BPSK modulation component as described with reference to FIGS. 9through 12.

It should be noted that the methods described above describe possibleimplementations, and that the operations and the steps may be rearrangedor otherwise modified and that other implementations are possible.Further, aspects from two or more of the methods may be combined.

Techniques described herein may be used for various wirelesscommunications systems such as code division multiple access (CDMA),time division multiple access (TDMA), frequency division multiple access(FDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), and other systems.A CDMA system may implement a radio technology such as CDMA2000,Universal Terrestrial Radio Access (UTRA), etc. CDMA2000 covers IS-2000,IS-95, and IS-856 standards. IS-2000 Releases may be commonly referredto as CDMA2000 1X, 1X, etc. IS-856 (TIA-856) is commonly referred to asCDMA2000 1xEV-DO, High Rate Packet Data (HRPD), etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. A TDMA system mayimplement a radio technology such as Global System for MobileCommunications (GSM).

An OFDMA system may implement a radio technology such as Ultra MobileBroadband (UMB), Evolved UTRA (E-UTRA), Institute of Electrical andElectronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, Flash-OFDM, etc. UTRA and E-UTRA are part of Universal MobileTelecommunications System (UMTS). LTE, LTE-A, and LTE-A Pro are releasesof UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, LTE-A Pro, NR,and GSM are described in documents from the organization named “3rdGeneration Partnership Project” (3GPP). CDMA2000 and UMB are describedin documents from an organization named “3rd Generation PartnershipProject 2” (3GPP2). The techniques described herein may be used for thesystems and radio technologies mentioned above as well as other systemsand radio technologies. While aspects of an LTE, LTE-A, LTE-A Pro, or NRsystem may be described for purposes of example, and LTE, LTE-A, LTE-APro, or NR terminology may be used in much of the description, thetechniques described herein are applicable beyond LTE, LTE-A, LTE-A Pro,or NR applications.

A macro cell generally covers a relatively large geographic area (e.g.,several kilometers in radius) and may allow unrestricted access by UEs115 with service subscriptions with the network provider. A small cellmay be associated with a lower-powered base station 105, as comparedwith a macro cell, and a small cell may operate in the same or different(e.g., licensed, unlicensed, etc.) frequency bands as macro cells. Smallcells may include pico cells, femto cells, and micro cells according tovarious examples. A pico cell, for example, may cover a small geographicarea and may allow unrestricted access by UEs 115 with servicesubscriptions with the network provider. A femto cell may also cover asmall geographic area (e.g., a home) and may provide restricted accessby UEs 115 having an association with the femto cell (e.g., UEs 115 in aclosed subscriber group (CSG), UEs 115 for users in the home, and thelike). An eNB for a macro cell may be referred to as a macro eNB. An eNBfor a small cell may be referred to as a small cell eNB, a pico eNB, afemto eNB, or a home eNB. An eNB may support one or multiple (e.g., two,three, four, and the like) cells, and may also support communicationsusing one or multiple component carriers.

The wireless communications system 100 or systems described herein maysupport synchronous or asynchronous operation. For synchronousoperation, the base stations 105 may have similar frame timing, andtransmissions from different base stations 105 may be approximatelyaligned in time. For asynchronous operation, the base stations 105 mayhave different frame timing, and transmissions from different basestations 105 may not be aligned in time. The techniques described hereinmay be used for either synchronous or asynchronous operations.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a digital signal processor (DSP), anapplication-specific integrated circuit (ASIC), a field-programmablegate array (FPGA) or other programmable logic device (PLD), discretegate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices (e.g., a combinationof a DSP and a microprocessor, multiple microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration).

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations.

Computer-readable media includes both non-transitory computer storagemedia and communication media including any medium that facilitatestransfer of a computer program from one place to another. Anon-transitory storage medium may be any available medium that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, non-transitory computer-readable media cancomprise RAM, ROM, electrically erasable programmable read only memory(EEPROM), compact disk (CD) ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any othernon-transitory medium that can be used to carry or store desired programcode means in the form of instructions or data structures and that canbe accessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor. Also, any connection isproperly termed a computer-readable medium. For example, if the softwareis transmitted from a website, server, or other remote source using acoaxial cable, fiber optic cable, twisted pair, digital subscriber line(DSL), or wireless technologies such as infrared, radio, and microwave,then the coaxial cable, fiber optic cable, twisted pair, DSL, orwireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,include CD, laser disc, optical disc, digital versatile disc (DVD),floppy disk and Blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

As used herein, including in the claims, “or” as used in a list of items(e.g., a list of items prefaced by a phrase such as “at least one of” or“one or more of”) indicates an inclusive list such that, for example, alist of at least one of A, B, or C means A or B or C or AB or AC or BCor ABC (i.e., A and B and C). Also, as used herein, the phrase “basedon” shall not be construed as a reference to a closed set of conditions.For example, an exemplary step that is described as “based on conditionA” may be based on both a condition A and a condition B withoutdeparting from the scope of the present disclosure. In other words, asused herein, the phrase “based on” shall be construed in the same manneras the phrase “based at least in part on.”

In the appended figures, similar components or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If just the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label, or othersubsequent reference label.

The description set forth herein, in connection with the appendeddrawings, describes example configurations and does not represent allthe examples that may be implemented or that are within the scope of theclaims. The term “exemplary” used herein means “serving as an example,instance, or illustration,” and not “preferred” or “advantageous overother examples.” The detailed description includes specific details forthe purpose of providing an understanding of the described techniques.These techniques, however, may be practiced without these specificdetails. In some instances, well-known structures and devices are shownin block diagram form in order to avoid obscuring the concepts of thedescribed examples.

The description herein is provided to enable a person skilled in the artto make or use the disclosure. Various modifications to the disclosurewill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other variations withoutdeparting from the scope of the disclosure. Thus, the disclosure is notlimited to the examples and designs described herein, but is to beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method for wireless communication at a userequipment (UE), comprising: establishing a connection with a basestation that uses a π/2 binary phase shift keying (BPSK) modulationscheme for at least a portion of wireless communications with the basestation; receiving, from the base station, an indication of a type ofreference signal sequence to be included within transmissions that usethe π/2 BPSK modulation scheme; generating a reference signal based atleast in part on the indication of the type of reference signalsequence; and transmitting the reference signal within communicationsthat use the π/2 BPSK modulation scheme.
 2. The method of claim 1,wherein the indication of the type of reference signal sequenceindicates a first type of reference signal sequence or a second type ofreference signal sequence.
 3. The method of claim 2, wherein the secondtype of reference signal sequence has a lower peak to average powerratio (PAPR) than the first type of reference signal sequence.
 4. Themethod of claim 2, wherein the second type of reference signal sequenceis a power deboosted version of the first type of reference signalsequence.
 5. The method of claim 2, wherein: the first type of referencesignal sequence is a Zadoff-Chu (ZC) sequence; and the second type ofreference signal sequence is a power deboosted ZC sequence or a π/2 BPSKdemodulation reference signal (DMRS) sequence.
 6. The method of claim 5,wherein the indication of the type of reference signal sequenceindicates the power deboosted ZC sequence and an amount of powerdeboosting to apply relative to data transmissions that use the π/2 BPSKmodulation scheme.
 7. The method of claim 1, wherein the indication fromthe base station is received via radio resource control (RRC) signaling.8. The method of claim 7, wherein the RRC signaling is a cell-specificRRC transmission that indicates the type of reference signal sequence tobe used by each UE in a cell served by the base station.
 9. The methodof claim 8, wherein the cell-specific RRC transmission comprises asystem information block (SIB) transmission, an other system information(OSI) transmission, or a remaining minimum system information (RMSI)transmission from the base station.
 10. The method of claim 7, whereinthe RRC signaling is a UE-specific RRC transmission that indicates thetype of reference signal sequence to be used by the UE.
 11. The methodof claim 1, further comprising: transmitting a capability indication tothe base station that indicates supported types of reference signals atthe UE, and wherein the indication of the type of reference signalsequence is received responsive to the capability indication.
 12. Themethod of claim 1, wherein the indication of the type of referencesignal sequence provides an initial type of reference signal sequence,and wherein the method further comprises: transmitting a capabilityindication to the base station that indicates supported types ofreference signals at the UE; receiving, responsive to the capabilityindication, a second indication of a type of reference signal sequenceto be included within transmissions that use the π/2 BPSK modulationscheme; and generating a reference signal based at least in part on thesecond indication of the type of reference signal sequence.
 13. Themethod of claim 1, wherein the generating the reference signalcomprises: identifying a plurality of allocated resource blocks and anumber of the allocated resource blocks for at least a firsttransmission using the π/2 BPSK modulation scheme; determining a bitsequence length for the reference signal corresponding to the number ofallocated resource blocks; and generating the reference signal based atleast in part on a bit sequence having the bit sequence length.
 14. Amethod for wireless communication at a base station, comprising:establishing a connection with at least a first user equipment (UE) thatuses a π/2 binary phase shift keying (BPSK) modulation scheme for atleast a portion of wireless communications with the first UE;transmitting an indication of a type of reference signal sequence to beincluded within transmissions of at least the first UE that use the π/2BPSK modulation scheme; receiving a transmission from at least the firstUE that uses the π/2 BPSK modulation scheme and that includes areference signal based at least in part on the indication of the type ofreference signal sequence; and demodulating the transmission based atleast in part on the reference signal.
 15. The method of claim 14,wherein the indication of the type of reference signal sequenceindicates a first type of reference signal sequence or a second type ofreference signal sequence.
 16. The method of claim 15, wherein thesecond type of reference signal sequence has a lower peak to averagepower ratio (PAPR) than the first type of reference signal.
 17. Themethod of claim 15, wherein the second type of reference signal sequenceis a power deboosted version of the first type of reference signalsequence.
 18. The method of claim 15, wherein: the first type ofreference signal sequence is a Zadoff-Chu (ZC) sequence; and the secondtype of reference signal sequence is a power deboosted ZC sequence or aπ/2 BPSK demodulation reference signal (DMRS) sequence.
 19. The methodof claim 18, wherein the indication of the type of reference signalsequence indicates the power deboosted ZC sequence and an amount ofpower deboosting to apply relative to data transmissions that use theπ/2 BPSK modulation scheme.
 20. The method of claim 14, wherein theindication of the type of reference signal sequence is transmitted viaradio resource control (RRC) signaling.
 21. The method of claim 20,wherein the RRC signaling is a cell-specific RRC transmission thatindicates the type of reference signal sequence to be used by each UE ina cell served by the base station.
 22. The method of claim 21, whereinthe cell-specific RRC transmission comprises a system information block(SIB) transmission, an other system information (OSI) transmission, or aremaining minimum system information (RMSI) transmission.
 23. The methodof claim 20, wherein the RRC signaling is a UE-specific RRC transmissionthat indicates the type of reference signal sequence to be used by thefirst UE, and wherein one or more other UEs use a different type ofreference signal sequence for transmissions that use the π/2 BPSKmodulation scheme.
 24. The method of claim 14, further comprising:receiving, from the first UE, a capability indication that indicatessupported types of reference signals at the first UE, and wherein theindication of the type of reference signal sequence is transmitted tothe first UE responsive to the capability indication.
 25. The method ofclaim 14, wherein the indication of the type of reference signalsequence provides an initial type of reference signal sequence, andwherein the method further comprises: receiving, from the first UE, acapability indication that indicates supported types of referencesignals at the first UE; selecting, responsive to the capabilityindication, the type of reference signal sequence to be included withintransmissions that use the π/2 BPSK modulation scheme; and transmittinga second indication to the first UE of a type of reference signalsequence to be included within transmissions of at least the first UEthat use the π/2 BPSK modulation scheme, wherein one or more subsequentcommunications with the first UE are based at least in part on thesecond indication.
 26. An apparatus for wireless communication at a userequipment (UE), comprising: a processor, memory coupled to theprocessor; and instructions stored in the memory and executable by theprocessor to cause the apparatus to: establish a connection with a basestation that uses a π/2 binary phase shift keying (BPSK) modulationscheme for at least a portion of wireless communications with the basestation; receive, from the base station, an indication of a type ofreference signal sequence to be included within transmissions that usethe π/2 BPSK modulation scheme; generate a reference signal based atleast in part on the indication of the type of reference signalsequence; and transmit the reference signal within communications thatuse the π/2 BPSK modulation scheme.
 27. The apparatus of claim 26,wherein the indication from the base station is received via radioresource control (RRC) signaling, and wherein the RRC signaling is aUE-specific RRC transmission that indicates the type of reference signalsequence to be used by the UE.
 28. The apparatus of claim 26, whereinthe instructions are further executable by the processor to cause theapparatus to: transmit a capability indication to the base station thatindicates supported types of reference signals at the UE, and whereinthe indication of the type of reference signal sequence is receivedresponsive to the capability indication.
 29. An apparatus for wirelesscommunication at a base station, comprising: a processor, memory coupledto the processor; and instructions stored in the memory and executableby the processor to cause the apparatus to: establish a connection withat least a first user equipment (UE) that uses a π/2 binary phase shiftkeying (BPSK) modulation scheme for at least a portion of wirelesscommunications with the first UE; transmit an indication of a type ofreference signal sequence to be included within transmissions of atleast the first UE that use the π/2 BPSK modulation scheme; receive atransmission from at least the first UE that uses the π/2 BPSKmodulation scheme and that includes a reference signal based at least inpart on the indication of the type of reference signal sequence; anddemodulate the transmission based at least in part on the referencesignal.
 30. The apparatus of claim 29, wherein the indication of thetype of reference signal sequence is transmitted via radio resourcecontrol (RRC) signaling comprising a UE-specific RRC transmission thatindicates the type of reference signal sequence to be used by the firstUE, and wherein one or more other UEs use a different type of referencesignal sequence for transmissions that use the π/2 BPSK modulationscheme.